The present invention relates to a ladder, especially for use in a manhole disposed in the ground, and has sidepieces with wall means that are provided with holes for rungs, whereby each rung is connected with a sidepiece via a sleeve that is disposed in one of the holes, with the sleeve having a base or end and, connected thereto, a sleeve body wall that is adapted to extend about the rung.
It is known to construct a ladder of sidepieces and rungs, with the connection between the rungs and sidepieces being effected by respective sleeves. The known sleeves can be produced pursuant to an injection molding process during the manufacture of the ladder. However, this manufacturing process is not suitable when hollow sections are used for the sidepieces. In order to achieve a permanent securement, the connections between the rungs and the sidepiece must on the one hand protect against withdrawal, and on the other hand must be rigid.
It has therefore already been proposed to effect connection of metallic sleeve-like intermediate pieces with the rungs and sidepieces by welding, riveting, or screw connections. However, ladders produced in this manner are relatively expensive.
Pursuant to a further proposed solution, it is known to replace the sleeve with an insert of elastic material, with mounting of the rung being effected on only the inner wall of the sidepiece and with a projection of the insert extending into an appropriate recess in the outer wall of the sidepiece. However, this ladder has not proven satisfactory in practice since the reliability against withdrawal of the rungs cannot be assured to a sufficient extent, and in addition no permanent rigid or twist-resistant mounting results, so that the ladder becomes unstable in a relatively short period of time. Furthermore, such a construction does not lend itself to automatic manufacture, since a surprisingly large number of rejects are produced.
It is furthermore known to make the sleeve that is used for the connection between the rung and the sidepiece in two parts, with one part being inserted from the outside into the rung hole of the sidepiece, and the other part being inserted from the inside. The sleeve part on the rung side is pressed over the rung, with the rung being deformed by an inwardly projecting edge. In addition, a force fit is established between the two parts of the sleeve. This is intended to produce a strong connection.
However, a drawback of this known sleeve is that again a relatively expensive configuration of the sleeve connection is provided, since during the manufacture two parts must be manipulated per rung connection, and in addition the pressing-on requires special tools. Furthermore, due to the deformation of the rung, the material is weakened, thus requiring a rung that comprises an extruded section to have relatively thick walls.
It is therefore an object of the present invention to provide a ladder of the aforementioned general type that is economical to produce, that offers an improved stability despite the fact that it has relatively thin parts, and that in addition provides the possibility of being able to mechanically carry out the rung/sidepiece connection without having a large number of rejects being produced thereby.